The control of unwanted pests, such as vegetative growth, is utilized to improve aesthetic appearance as well as removing the noxious pests or vegetation. In the past, one of the most common methods of controlling such unwanted growth was through the application of pesticides to the vegetation. Such pesticides, particularly herbicides, were commonly applied by spraying a liquid herbicide or through spreading of powders or granules. However, in recent years the use of herbicides has met with increased resistance owing to environmental, health and safety concerns. Herbicides can contaminate soil, air, groundwater and desirable vegetation and may cause health problems to those exposed to such chemicals. In view of these problems, the use of herbicides has been restricted or in some cases completely banned in many jurisdictions.
Another common method of controlling unwanted vegetative growth is through physical removal of the plant. This method has drawbacks in that it is time consuming, labor intensive, physically demanding and disturbs the soil surface, exposing more weed seed. In addition if all of the plant material is not removed and some of the root structure remains, the plant may regrow and have to be removed yet again.
As environmental concerns are reducing the use of pesticides, and the prohibitive costs and inefficiencies of manual weeding become apparent, the use of heat and/or steam for vegetation control is gaining popularity. Heat coagulates plant protein, destroying plant cells, disrupting vascular flow and respiration. Also waxy protective leaf coatings are removed, promoting dehydration and death of the plant. Studies have shown that exposure to 80 C. (176 F) for one second can kill vegetation. Also steam or moist heat is superior to flame or dry heat for weeding as damp air transfers heat more readily, and is easier to apply in a downward direction (hot, dry air rises and diffuses faster). Steam or moist air is less likely to cause accidental fires and thus is safer than flame or dry heat.
Recently, the use of heat to kill unwanted vegetation has been utilized and a number of apparatus to apply heat, generally in the form of hot water or steam have been proposed. Examples of such apparatus are shown in U.S. Pat. Nos. 5,385,106, 5,430,970, 5,927,601, 5,946,851, 6,029,589, 6,047,900, and 6,321,037, PCT Patent Application WO 00/22926 and New Zealand Patent Application 237,524 among others.
U.S. Pat. No. 5,385,106 describes cart, backpack, and vehicle mounted apparatus which utilize propane or electricity to heat water in a chamber which is then delivered along piping for application to the plant. One problem with this apparatus is that the heated water must travel along the tubing before application to the plant which may cause some cooling of the water.
U.S. Pat. No. 5,430,970 describes an apparatus including an endless, ground-engaging belt, or apron, disposed immediately aft of a hot water spray. When hot water is sprayed on the weeds and undergrowth, the sprayed vegetation is not only compressed by the apron, but also heat from the water is retained therein, insulated from ambient conditions by the apron.
U.S. Pat. Nos. 5,927,601 and 6,047,900 describe a vehicle mounted apparatus for the application of pressurized hot water to vegetation particularly along roadside berms. The apparatus has a boiler arranged to heat water supplied under pressure from a water tank and then pass the heated water under pressure to an applicator head. Once again, the heated water must travel along extensive piping which can result in cooling of the water before it reaches the plant.
U.S. Pat. No. 5,946,851 describes a weed killing apparatus having a hollow chamber with an air inlet and an open hot air outlet, a source of compressed air to provide an air flow and a burner assembly for heating the air so that the air exits from the outlet as a blast of hot air and a means for introducing moisture to the heated air so that the plants are wetted and heated to kill them.
U.S. Pat. No. 6,029,589 describes a portable steam weed killing apparatus having an electrically powered steam generator which generates steam and delivers it through flexible tubing to a weed cover placed over the undesired plant. The apparatus, being electrically powered is limited in the area which can be treated which is dependent upon the length of extension cords and is thus not suitable for large scale operation.
U.S. Pat. No. 6,321,037 describes a hand held dispenser of hot water intended for weed control. The apparatus has a handle containing a hose connection for connecting to a domestic water supply, a flow regulator, a heating tube, an exit tube, and a nozzle. The handle is connected to a tube which contains a main electric heating element for heating the water as it flows from the bottom to the top of the apparatus before being piped through the exit tube to the nozzle. Once again, as the apparatus is powered by household electrical supply and connected to the domestic water supply, the range of operation of the apparatus is limited.
PCT Patent Application No. WO 00/22926 describes a large tractor mounted unit which mixes hot gases and steam for application to weeds in agricultural applications. The mixture of hot gases and steam is mixed after the steam generator using pressure and then applied to the desired area. This apparatus is complicated to manufacture and operate.
New Zealand Patent Application No. 237,524 describes a backpack mounted portable steam generator that generates steam within the handle of the applicator and delivers the steam by means of a tube to the target area. This apparatus suffers disadvantages in that the user may be exposed to the hot gases at the handle and the length of the tube may result in cooling of the steam, thereby reducing effectiveness.
There thus remains a need for a simple, lightweight, portable, and cost effective apparatus for applying steam, hot water or hot water vapor and heat to unwanted vegetation to kill the vegetation and which utilizes minimal energy in its operation.